1. Field of the Invention
The present invention relates to a moisture curable composition suitable for use as an adhesive, a sealing material or the like which is required to be transparent.
2. Description of Related Art
Currently, a composition produced by normally blending an inorganic powder such as calcium carbonate or the like into a polymer having reactive silicon groups has been used in practice as an adhesive, a sealing material, or the like. The effect of blending the inorganic powder in this case is to give cohesive power to the polymer mainly having the reactive silicon groups, and to improve the adhesiveness on the interface with an adherend.
In recent years, when a transparent substrate such as glass, polycarbonate, acrylic resin or the like is adhered or sealed with an adhesive or a sealing material, the adhesive or the sealing material is also required to be transparent from the design viewpoint. However, there has been no transparent polymeric composition having reactive silicon groups which satisfies sufficient property of an adhesive or a sealing material.
In order to give the transparency to an adhesive and a sealing material, there are the following two methods: (1) a method without blending a filler; and (2) a method of blending an inorganic filler having a small grain diameter. However, the method (1) implies problems related to the basic properties such as the insufficient adhesiveness. The method (2) has problems that if a blended inorganic filler has a grain diameter of 0.01 .mu.m or more, the resultant composition can not provide a sufficient transparency, and that if the grain diameter is smaller than 0.01 .mu.m, it exhibits a viscosity which is abruptly increased with a small amount of the inorganic filler being added, a poor storage stability, and so on.
As a solvent-based adhesive which has excellent transparency without blending a filler, urethane adhesives, polyvinyl chloride adhesives and the like are placed on the market. However, when transparent adherends are adhered each other using the solvent-based adhesive, for its flowability there are formed starved areas due to air between the adherends and the adhesive, unless the adherends are adhered with a fair amount of solvent remaining therein. Such starved joints lead disadvantageously to opaque portions existing at adhering areas. The solvent included in the adhesive may also unfavorably dissolve plastics and bring about some cracks on adherends.